National Double Cheeseburger Day is observed worldwide every September 15, celebrating the deliciousness of double cheeseburgers, which consist of two juicy patties and typically two slices of cheese. The cheeseburger, a variation of the hamburger, became popular in the United States in the late 19th century, with the addition of cheese becoming common in the 1920s. The first cheeseburger is often attributed to Lionel Sternberger, who created it in 1924 at his father's sandwich shop in Pasadena, California. On this day, many people indulge in double cheeseburgers from various fast food chains, including McDonald's, Burger King, and Five Guys, or enjoy homemade versions with friends. Participants are encouraged to share photos of their meals on social media using hashtags like #NationalDoubleCheeseburgerDay. This holiday precedes National Cheeseburger Day, which is celebrated just three days later.